German Patent No. 37 33 849 discloses a machine vise using a force amplifier exerting in clamping position a high pressure onto the spindle nut provided at the movable jaw resulting in a corresponding reaction force in the fixed jaw This may cause a bending of the body such that the opposing clamping surfaces of the fixed and movable jaws are no more parallel to each other, a situation considerably reducing the capability of fully clamping the workpiece.
German Patent No. 34 37 403 discloses a machine-tool vise comprising a force amplifier arranged below the movable jaw in a fully retracted position of the latter. A common drive means for the movable jaw and the force amplifier is attached to the machine vise projecting considerably from the body thereof. Final clamping by activating the force amplifier exerts a high pressure onto the screw spindle supported in the body causing a bending thereof resulting in a loss of the parallelity of the opposing clamping surfaces of the fixed and movable jaws. A similar machine vise is disclosed in U.S. Pat. No. 4,899,999.
U.S. Pat. No. 4,098,500 discloses a machine vise without force amplifier having the movable jaw split into an upper part and a lower part the lower part having formed thereon the spindle nut and an insert portion loosely received in a recess of the upper part. The insert portion and the recess have opposing surfaces inclined at an angle of about 45.degree. in respect of the screw spindle axis. By means of a screw the opposing inclined surfaces of the insert portion and the recess are fixedly urged against each other. A vertical screw fixes the position between the upper and lower parts. Thus, there is no resiliency between them resulting in a considerable friction during movement of the movable jaw.
U.S. Pat. No. 4,043,547 discloses a machine vise without force amplifier, similar to that of the machine vise just described, with the additional feature of having a spring washer arranged between said opposing inclined surfaces.